Australia in Summer (December-February) 2011-12

In Brief

Summer 2011/12 was generally wet over large parts of Australia, with the exception of parts of the tropical north and southeast of the country. Particularly heavy falls over northern NSW and southern Queensland resulted in moderate to major flooding over parts of those regions.

Maximum temperatures were generally close to normal over much of the country, with the WA interior and parts of eastern Australia experiencing a cool summer. Minima were generally above normal across much of southern Australia, and parts of the far tropical north, while central to northern regions were generally below normal.

Temperatures

Maximum temperatures averaged across Australia were 0.55°C below normal, 11th coolest in 62 years of record. Most of the country was close to normal, with parts of the west and east significantly cooler than normal. NSW had a particularly cool summer, with an anomaly of −1.71°C, the 2nd coolest on record. Conversely, Tasmania had a particularly warm summer, measuring its 3rd warmest summer.

Temperatures more than 1°C cooler than normal were recorded over the WA interior extending into northwest SA, as well as southern Queensland and the northeastern half of NSW. Anomalies of −3 to −4°C were recorded in an area from Charleville in Queensland, south to Dubbo in NSW. Large parts of these regions were in the bottom decile of maximum temperature records, with a large area of decile 1 in the WA interior, and also covering much of southern Queensland and northeast NSW. A large part of northeast NSW recorded its coolest summer on record (29% of the NSW area). Heavy rainfall during summer was a major contributor to these low maximum temperatures.

Small pockets of maximum temperatures 1°C above normal were measured across coastal WA, small areas of the northern NT, an area near the SA-Victoria border and most of Tasmania. Coastal parts of WA, the western Top End of the NT and the northern and western areas of Tasmania recorded maxima in the top decile.

Tasmania experienced a very warm end to summer, with maxima on the 25th and 26th of February topping 30°C across most of the state. Parts of the southeast exceeded 36°C on both days, and some sites recorded their hottest daily February temperatures on record. In mid to late December a heatwave was experienced across the Pilbara coast, with the hottest December day in WA set on the 21st at Roebourne, near Karratha in WA, measuring 49.4°C. This was the 2nd hottest December day for Australia, and the highest temperature in Australia since 1998.

Summer minimum temperatures were 0.32°C below normal for Australia, 15th lowest of 62 years (the coolest summer minima for the past 10 years). Generally, the southern coastal regions of Australia and the far northern tropics had warmer than normal overnight minima, while much of central and northern Australia had cooler than normal overnight temperatures. State-wise, Tasmania recorded its 4th warmest overnight temperatures (anomaly of +1.04°C) and Victoria its 10th warmest. Conversely, Queensland had its 8th coolest minimum temperatures (lowest since 1974), and the NT its 10th (lowest since 1978).

Overnight temperatures were at least 1°C cooler than normal over the central WA interior, over parts of the NT-Queensland border, and inland over parts of the Queensland-NSW border. Most of this area measured minima in the lowest decile. Conversely, overnight temperatures more than 1°C warmer than normal were measured over the western WA coast, parts of the SA and Victorian coastlines and northern Tasmania. Tasmania, southern Victoria, and large parts of western WA had minima in the warmest decile, with a small area of coastline near Perth recording its warmest overnight summer temperatures on record.

Rainfall

Australian area-averaged rainfall for summer 2011/12 was 241.2 mm (16% above average), the 22nd wettest of 112 years. Generally, most of the country received a wetter than normal season, with the exception of parts of the tropical north and southeast Australia. NSW had a very wet season, measuring its 9th wettest summer on record, with 261.0 mm (53% above average). Likewise, the Murray Darling Basin was also very wet, recording its 6th wettest summer (68% above normal).

Above average rainfall covered most of the southern two-thirds of the Australian mainland. The southwest and central parts of WA received above average falls, as did most of SA, parts of the southern NT, and north central Victoria. Southern Queensland and NSW had heavy falls throughout the summer, resulting in much of the coastal and inland areas recording rainfall in the top decile. The heavy rainfall, in part a result of La Niña conditions in place since spring, caused major flooding over broad areas of northern NSW and southern inland Queensland from late January onwards.

Below average falls were generally confined to small pockets of Australia, with the northern Kimberley in WA and large parts of the northern NT recording below average falls. Further south, an area near the SA-Victoria border received below average falls, as did Tasmania and a small area of southeast WA. The Top End of the NT had a long stretch of dry days during early January, with Darwin recording 10 days of no rain from the 4th to the 13th of January, the longest dry stretch in January/February since 1973.

During summer 2011/12, there were six tropical cyclones in the Australian region. Of these, three passed over the Australian continent, having a localised effect on rainfall. Tropical Cyclone Grant, crossed the Top End of the NT in late December, producing heavy falls near Katherine, with the highest total of 385 mm at Edith Falls Ridge on the 27th of December. In mid-January, Tropical Cyclone Heidi crossed the Pilbara coast near Port Hedland in WA, with several falls in excess of 100 mm. Pardoo, located near Port Hedland, recorded 168.5 mm on the 11th of January. Lastly, in early February the remains of Tropical Cyclone Iggy crossed the WA coast, south of Geraldton, with falls in excess of 50 mm.

Notes

The Seasonal Climate Summary is prepared to list the main features of the weather in Australia
using the most timely and accurate information available on the date of publication; it will generally not be updated.

This statement has been prepared based on information available at
12 pm on Thursday 1 March 2012.
Some checks have been made on the data, but it is possible that results will change as new information becomes available,
especially for rainfall where much more data becomes available as returns are received from volunteers.

Long-term averages in this statement and associated tables are for the period 1961 to 1990 unless otherwise specified.

In the tables, fractional ranks denote tied values.

A new area-averaging method was adopted for rainfall in May 2009. Current and historical totals for Tasmania are substantially higher than under the old scheme, but differences for other states, and nationally, are negligible.
The rankings and departures from mean shown here use the new method.